This application is based on and claims priority to Japanese Patent Application Nos. Hei 10-344,741, filed Dec. 3, 1998, Hei 10-344,745, filed Dec. 3, 1998, and Hei 11-215,896, filed Jul. 19, 1999, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to alloy components having wear surfaces and to methods of manufacturing such components. More particularly, the present invention relates to aluminum alloy components having expandable wear surfaces formed by plating.
2. Description of Related Art
Many components of vehicles are unnecessarily heavy. These components decrease fuel economy and can lead to premature aging of suspension components as well as to poor handling characteristics of the vehicle. Accordingly, decreasing the weight of vehicles has become a goal across all lines of vehicles.
Some examples of such components that have been reduced in weight are connecting rods, tappets and rocker arms of engines. A further example of such a component is a brake disc of a disc brake device mounted on vehicles such as automobiles and motorcycles. Specifically, there is a high demand for brake discs that have as light a weight as possible in order to improve both running performance and fuel consumption. One idea for achieving the decreasing the weight of the brake disc is to use an aluminum alloy for forming a plate-like part (hereinafter, the plate-like part will be called xe2x80x9cbrake disc bodyxe2x80x9d) which is to be fixed to a hub.
Because most aluminum alloys are relatively soft materials, when the brake disc body is formed of an aluminum alloy, an annular ring made of an iron-containing metal is typically bonded to a surface of the brake disc body to form a frictional surface. This metal increases the life of the brake disc by providing a harder wear surface for the brake disc. Such a brake disc is disclosed, for example, in JP-A-H5-26268.
The brake disc disclosed in the above publication includes a brake disc body formed of an aluminum alloy and having a front surface portion that a brake pad selectively engages. An annular ring made of cast iron is secured to the brake disc body by friction welding or by an alfin process.
Since an aluminum alloy has a greater coefficient of thermal expansion than that of iron-containing metal such as cast iron, the use of a construction in which a cast iron disc is bonded to an aluminum alloy brake disc body is apt to cause warping, bending or flexing of the brake disc due to thermal stresses generated by temperature increases during braking. Such warping, bending and flexing, under extreme conditions, can result in separation of the iron disc from the brake disc body.
Moreover, in order to affix the cast iron ring to the aluminum alloy brake disc body, a specific bonding device is required and, hence, the associated manufacturing costs increase.
In other applications, such as with aluminum alloy connecting rods, valve lifters, tappets and rocker arms of engines, it becomes necessary to improve the wear resistance of a wear surface thereof. In particular, when an aluminum alloy is used for the parts and when the parts will be used under high temperature conditions, the high thermal load practically mandates an improvement to the aluminum alloy wear surfaces.
Accordingly, one object of the present invention involves the fabrication of an aluminum alloy part having a wear surface that has a high wear-resistance. Another object of the present invention involves providing an aluminum alloy part which is subjected to a high thermal load, such as an engine part, and which has a slide surface having much improved wear resistance. It is a further object of the present invention to provide an aluminum alloy brake disc body for a disc brake device that has a metal layer of a high wear-resistance and, yet, which generates reduced thermal stresses and requires reduced manufacturing costs.
Accordingly, one aspect of the present invention involves a method of forming an expandable wear surface on an aluminum alloy component. The method comprises preparing the aluminum alloy component and then plating the component with a layer of wear resistant material. A network of cracks is formed through the layer of wear resistant material such that the network of cracks comprise multiple fragments. Each fragment preferable has an interstitial size defined by as a diameter of a circle that is inscribed between the cracks defining any single fragment.
Another aspect of the present invention involves an aluminum alloy part having a plated wear resistant surface. The part generally comprises an aluminum alloy substrate and a plated wear resistant surface covering at least a portion of the substrate. The wear resistant surface has a plurality of wear resistant surface fragments that are separated from one another by cracks. The cracks form a network of cracks.
For the purpose of summarizing the invention and the advantage achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all of the objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize an invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. In addition, further aspects, features and advantages of the present invention will become apparent from the detailed description of the embodiments that follow.